Friday, October 31, 2014

The Fairness of the AFL Fixture

In yesterday’s
post I rated the difficulty
of each AFL team’s draw in 2015. Each year there is a fair bit of variation
in the difficulty of the draw between teams; for example, in 2015 I consider
the club with the easiest draw, West Coast, to have a goal a game advantage
over the club with the hardest draw, Port Adelaide.Over at the FootyMaths
Institute it has been proposed that a fairer 2015 fixture would have each
team play opponents of roughly the same level throughout the year. To achieve
this it has been suggested splitting the teams into three conferences of
roughly equal strength as follows, with each team playing the teams in their
own conference twice and every other team once.Conference
1: Teams ranked 1, 6, 7, 12, 13, 18.

Conference
2: 2, 5, 8, 11, 14, 17.

Conference
3: 3, 4, 9, 10, 15, 16.That seems
about as fair as you can get to me. (Ladder positions can be misleading of
course, but I doubt the AFL is going to do a fixture based on a Power Rankings
system!) A comment I made was that the conferences need only be notional; that
is, teams could be split into conferences for the purposes of the fixture, but
the ladder is calculated according to the same method as it always was.Yesterday I
wondered how far the actual AFL fixture deviated from this ‘fair’ system. To
compare the two, let’s see how each team’s draw would be rated under the
FootyMaths system. I am going to assume that the FootyMaths fixture would
result in no net home ground advantage to any team over the course of the year.
This probably will not strictly hold because of things like Geelong playing in
Geelong against Melbourne clubs, but unless you get savaged like St. Kilda did
for 2015, net home ground advantage is generally the least important component of
a club’s fixture.Here are the
results:

Overall

Effect
of not playing own team

Effect
of teams played twice

Sydney

78.0

33.8

44.2

Hawthorn

68.0

34.6

33.4

Port Adelaide

41.8

21.5

20.3

North Melbourne

28.8

9.2

19.6

Adelaide

24.2

16.7

7.5

Fremantle

21.9

15.6

6.3

Essendon

18.2

3.9

14.3

West Coast

17.5

13.4

4.1

Richmond

11.8

6.5

5.3

Geelong

4.8

7.1

-2.2

Carlton

1.3

-4.6

5.8

Gold Coast

-13.7

-12.0

-1.6

Collingwood

-26.5

-12.7

-13.8

Western Bulldogs

-42.7

-20.8

-21.9

GWS

-51.4

-21.0

-30.3

Brisbane

-54.2

-22.4

-31.7

Melbourne

-57.0

-27.9

-29.1

St. Kilda

-70.9

-40.7

-30.3

What the - ?
This seems to be more uneven than the current AFL fixture! Note that the
easiness of each’s team fixture is essentially determined by their ranking.
Lower-ranked teams are now hit by a double whammy: not only are they the only
team that do not get to play themselves when each team plays each other once,
they are also the only team in their ‘conference’ that do not get to play
themselves twice either.

We seem to
have hit on something crucial here about what constitutes a ‘fair’ fixture. On
one hand you could argue that the AFL should compensate for lower-ranked teams
not being able to play themselves and give them easier teams to play to make up
for it (although they seem to have overcompensated on this point). On the other
hand you could argue that a ‘fair’ system should abstract from this effect.

Note here
that a ‘fair’ fixture could result in teams having draws of varying difficulty.
Perhaps Sydney and Hawthorn might have the easiest draws under the FootyMaths
system because they do not have to play themselves, but this does not
necessarily mean that the fixture is not ‘fair’.

What happens
if we take out the effect of not having to play your own team? (I have also taken
out the net home ground advantage from the AFL fixture as well.)

FMI
fixture

AFL
fixture

Gold Coast

10.4

-8.4

North Melbourne

10.4

-19.7

Essendon

10.4

-0.8

Carlton

10.4

19.7

Sydney

10.4

-63.8

St. Kilda

10.4

93.2

Hawthorn

-1.1

-96.2

Port Adelaide

-1.1

-101.4

Collingwood

-1.1

27.7

Richmond

-1.1

-17.9

Western Bulldogs

-1.1

77.0

Melbourne

-1.1

107.5

GWS

-9.3

72.5

Fremantle

-9.3

-38.1

Geelong

-9.3

-88.7

Adelaide

-9.3

-24.2

West Coast

-9.3

27.8

Brisbane

-9.3

33.9

Standard deviation

8.3

63.6

Now that
seems better. Basically the difference between the hardest ‘conference’ and the
easiest one is less than a point a game. For the AFL fixture the difference
between the hardest draw and the easiest one is about two goals a game.

Personally I
like the FootyMaths proposal; it seems to me about as fair as you can get with
each team playing 22 matches. It might be even better than having a 17 round
season.